The Senate committee responsible with oversight of Medicare and much of the health reform law is going to look a lot different in 2013, with at least four of its members retiring at the end of the year and others possibly facing tough elections.

The Senate Finance Committee — arguably one of the most influential on Capitol Hill — could look less centrist and more partisan, regardless of which party controls the Senate after the November elections.

Democratic Sens. Kent Conrad of North Dakota and Jeff Bingaman of New Mexico and Republican Sen. Olympia Snowe of Maine — three of the highest-ranking committee members from both parties — all plan to retire at the end of the year. Each has a record as a moderate, a bridge builder, or both.

Republican Sen. Jon Kyl of Arizona is leaving, too. He’s much more partisan than the other departing senators, but he also has a deep health care policy background that has made him a key player in deficit reduction talks and in the discussions about replacing the broken Medicare payment formula.

The retirements mean a loss of some of the panel’s institutional knowledge on some of the nation’s thorniest issues: Medicare, taxes, trade and the economy.

Sen. Chuck Grassley (R-Iowa), a former chairman of the committee, said he expects the panel to be more partisan after the four retire.

“I think it would be more conservative — definitely on the Republican side,” Grassley told POLITICO. “Maybe a little less conservative on the Democrat side. If Sen. [Max] Baucus is the leader of it, though, he’s going to do what he can to make sure it functions, because that’s his philosophy. And I’ll be there to help him.”

The committee had a big influence on the shaping of President Barack Obama’s health reform law, pulling it to the center and jettisoning some liberal priorities — including the public option — that many Democrats had wanted.

The Finance Committee is one of the most sought-after assignments on Capitol Hill, especially with such a high-profile role in the national discussion of deficits and entitlements — a focus that is unlikely to change much in 2013. Leaders typically use the assignments to reward loyalty and longevity.

But Utah Sen. Orrin Hatch, the top Republican on the panel, suggested that leadership could choose not to fill all four of the slots that will open up — or more, depending on the election outcome.

“I don’t know what the leadership will decide to do. They may shorten the number of people in the committee or just add some people to it,” Hatch told POLITICO. “It depends a lot on who is in the majority next time, too.”

The idea is that it’s easier to wrangle a smaller number of people. Plus, the committee added members in recent years, and with an even number of retirements from both sides of the aisle, the departures could shrink its numbers without having to push people off.

But it’s likely that each side will get to appoint at least one member.

On the Republican side, Sen. Johnny Isakson of Georgia is widely assumed to be the next to get a prized Finance post. Sen. Rob Portman of Ohio, a former White House budget director, is thought to be a likely contender, too.

On the Democrats’ side, Sens. Mark Begich of Alaska, Michael Bennet of Colorado and Bob Casey of Pennsylvania are the type of pragmatists that could be tapped to serve. And Sens. Sherrod Brown of Ohio and Sheldon Whitehouse of Rhode Island are also thought to be in the mix, according to Hill aides and health care lobbyists.

“Some saw Casey’s involvement in the payroll tax issue as the sort of trial run for how he might work on Finance. He was a real constructive part of the payroll conference,” a senior Senate aide said, noting that Begich and Bennet fit the same mold.

The model of the typical Finance member — with a few notable exceptions — is a pragmatist and a bridge builder in the style of Bingaman, Grassley, John Kerry and Mike Crapo.

“These are guys who want to try to get to yes, even in a politically toxic environment,” the aide said. “I would think leadership on both sides would want to appoint similar members moving forward.”

But the traditional pragmatist is a dying breed in the Senate, a former committee aide said. As more and more of the across-the-aisle types leave the Senate, their replacements have often come from more partisan ranks.

“That’s really beginning to impact the Finance Committee now,” the former aide said. “And it affects the ability of the Finance Committee to do its job when it’s required.”

Because committee members tend to stay put, the political mix could have a lasting effect on legislation.

“Whoever gets appointed now will get to shape the makeup of the committee for a long time,” the former aide said. “That’s why the change in deal makers to whoever takes their place will matter for a long time.”

On the Republican side, the retirements put Crapo next in line behind Hatch, since term limits prevent Grassley from serving as the committee’s top Republican again. On the Democratic side, West Virginia Sen. Jay Rockefeller remains behind Baucus, followed by Kerry and Ron Wyden of Oregon.

To be sure, the Senate Finance Committee hasn't been constantly busy with markups. Over the past two congressional sessions, the panel has held only a handful of markups - though they include a lengthy one for the Senate's health reform package. The others included trade bills and a small tax provision.

But that may underscore the panel’s importance because many of the deficit-cutting groups that have gathered in recent years have drawn heavily from its members. Plus, divided government has diminished the role of every committee as party leaders have increasingly become the ultimate brokers of legislation. And many of the bills that hit the floor directly have Finance work in them.

As members of the committee leave, they take with them a wealth of knowledge that doesn’t quickly translate to newer members, said Dean Rosen, a partner with the lobbying firm Mehlman Vogel Castagnetti.

“Whenever you lose those long-serving members, regardless of their political stripes, you’re losing a ton of experience,” he said.

Rosen added that the breadth of the Finance Committee makes it especially hard to replace members who leave. “The jurisdiction is so broad — taxes, health, Medicare, Medicaid, trade—that it’s difficult to replace that expertise right away,” he said.

“My sense is, you want people who are going to be team players,” Rosen said. “I’m sure both leaders want that, particularly because the issues involved really have been — and will be — the most contentious politically and substantially thorny.”

CLARIFICATION: This story has been updated to clarify the committee activities over the last two congressional sessions.